JP2006276390A - Optical coupler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce coupling loss when a plurality of input signals are to be coupled. <P>SOLUTION: This optical coupler 1 has a plurality of incident waveguides 21-1 to 21-n, a coupling section 23 which optically couples the incident waveguides and a light emitting waveguide 22 which is connected to the coupling section. The refractive index of a clad 32 of the light emitting waveguide and the refractive index of at least a portion of a substrate 10 are regulated to be smaller than the refractive index of a clad 31 (the substrate 10) of the incident waveguide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical coupler that combines and enhances the power of light, for example.

  In the fields of optical communication, medical industrial equipment, and consumer equipment, optical couplers that combine and enhance the power of light are widely used.

As an optical coupler, for example, Patent Document 1 discloses an optical coupler provided with an arbitrary number of channel-type optical waveguides and slab waveguides on the surface of a substrate.
Japanese Patent Laid-Open No. 11-231157

  In Patent Document 1, in an optical coupler, a plurality of channel type optical waveguides and a multimode optical fiber are coupled by a slab type waveguide, and the waveguide width of the multimode optical fiber is determined by the channel type waveguide to be coupled. It is described that it increases with the number.

  However, the optical coupler of Patent Document 1 has a problem that the width of the multimode optical fiber becomes extremely large as the number of channels to be coupled increases. Furthermore, when a fiber having the same core diameter as that on the input side is used on the output side, there is a problem in that the coupling efficiency between the waveguide and the fiber is deteriorated and loss is increased.

  An object of the present invention is to reduce coupling loss in an optical coupler that combines and enhances the power of light.

The present invention has been made based on the above problems, a base material, a core region formed on the base material, a cladding region that gives a predetermined refractive index difference to the core region,
The core region includes a plurality of incident waveguides, a coupling portion that couples the plurality of incident waveguides, and a smaller number of outgoing waveguides than the incident waveguides connected to the coupling portion. In the optical coupler in which the total sum of the widths of the incident waveguides is larger than the total sum of the widths of the output waveguides, the refractive index of a part or all of the cladding on the output waveguide side is An optical coupler characterized by having a refractive index smaller than that is provided.

  According to the present invention, since the “light confinement action” on the optical coupling side, that is, the output side waveguide is strengthened, the coupling loss is reduced. Further, it is not necessary to secure the width of the output side waveguide core more than necessary, and the size of the optical coupler is also reduced.

  Further, the present invention has been made based on the above problems, and includes a base material, a core region formed on the base material, and a cladding region that gives a predetermined refractive index difference to the core region. The core region comprises a plurality of incident waveguides, a coupling portion for coupling the plurality of incident waveguides, and a smaller number of output waveguides than the incident waveguides connected to the coupling portion; In the optical coupler in which the total sum of the widths of the incident waveguides is larger than the total sum of the widths of the output waveguides, the refractive index of a part or all of the cores on the output waveguide side is the refractive index of the cores of the input side waveguides. An optical coupler characterized by being larger than the rate is provided.

  According to the present invention, since the “light confinement action” on the optical coupling side, that is, the output side waveguide is strengthened, the coupling loss is reduced. Further, it is not necessary to secure the width of the output side waveguide core more than necessary, and the size of the optical coupler is also reduced.

  Furthermore, the present invention has been made on the basis of the above problems, and includes a base material, a core region formed on the base material, and a cladding region that gives a predetermined refractive index difference to the core region. The core region comprises a plurality of incident waveguides, a coupling portion for coupling the plurality of incident waveguides, and a smaller number of output waveguides than the incident waveguides connected to the coupling portion; In the optical coupler in which the total sum of the widths of the incident waveguides is larger than the total sum of the widths of the output waveguides, the refractive index of a part or all of the cladding on the output waveguide side is refracted by the clads of the incident side waveguides. The optical coupler is characterized in that the refractive index of a part or all of the core on the exit waveguide side is smaller than the refractive index, and is larger than the refractive index of the core of the incident side waveguide.

  According to the present invention, since the “light confinement action” on the optical coupling side, that is, the output side waveguide is strengthened, the coupling loss is reduced. Further, it is not necessary to secure the width of the output side waveguide core more than necessary, and the size of the optical coupler is also reduced.

  According to the optical coupler of the present invention, the coupling loss is reduced.

  In addition, the width of the optical fiber connected to the output side is prevented from becoming extremely large.

  Therefore, the size of the optical coupler is reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an example of an optical coupler to which an embodiment of the present invention is applied.

As shown in FIG. 1, an optical coupler 1 includes a substrate 10 mainly composed of, for example, Si (silicon) or SiO ₂ (silicon oxide), and a light beam formed by patterning a predetermined shape on the substrate 10. And a waveguide structure 20. In the example shown in FIG. 1, the optical waveguide structure 20 is directly provided on the substrate 10, but a layer having a uniform refractive index called an underclad may be formed on the upper surface of the substrate 10.

  The periphery of the optical waveguide structure 20 is covered with a member that functions as a cladding layer 30 for making the optical waveguide structure 20 usable as a core. In addition, when an under clad layer is provided, the clad layer 30 is called an upper clad for identification.

  A plurality of incident side waveguide cores 21-1 to 21-n are provided on the incident side of the optical waveguide structure 20. A single exit-side waveguide core 22 is formed on the exit side of the optical waveguide structure 20. The incident-side waveguide cores 21-1 to 21-n and the emission-side waveguide core 22 are optically coupled to each other by the optical coupling portion 23 defined at a predetermined position on the substrate 10 (or on the underclad). Are combined.

  The cladding layer 30 includes an incident-side cladding 31 that covers the incident-side waveguide cores 21-1 to 21 -n from the boundary C with a region C indicated by a dotted line near the optical coupling portion 23 of the optical waveguide structure 20 as a boundary. The optical coupling unit 23 is used as a boundary, and the output side cladding 32 covers the output side waveguide core 22 side from the boundary C. Note that the position of the boundary C that divides the clad layer 30 into the incident-side clad 31 and the outgoing-side clad 32 is not necessarily matched with high accuracy with respect to the optical coupling portion 23, and in particular, the incident-side waveguide core 21. It is sufficiently allowed to deviate toward (1 to n).

Of the clad layer 30, the output-side waveguide clad 32 is defined to have a refractive index n lower than that of the incident-side waveguide clad 31. That is, if the refractive index of the incident side waveguide cladding 31 is n ₃₁ and the refractive index of the emission side waveguide cladding 32 is n ₃₂ ,
n ₃₁ > n ₃₂
It is.

If the refractive index n of the incident-side waveguide cores 21-1 to 21-n and the outgoing-side waveguide core 22 is equal, when the refractive index of the outgoing-side waveguide core ₂₂ is denoted as n22,
n ₂₂ > n ₃₂
It is.

That is, the refractive index n ₃₂ of the outgoing side waveguide clad 32, the refractive index of the refractive index n ₂₂ and the incident side waveguide clad 31 of the outgoing side waveguide core 22 may be lower than the respective n _31.

Therefore, the material of the output side waveguide clad 32 can be, for example, air (refractive index n _AIR ≈1). In this case, the output side waveguide cladding 32 is not necessary. As a clad, there is a lower clad (the base material 10 in the example of FIG. 1). However, as described later with reference to FIG. 7, the relationship between the refractive index of the core and the clad described above is the same as that of the clad on the output side. All or a part of the refractive index may be lower than the refractive index of the clad on the incident side.

More specifically,
Respective refractive indexes of the incident-side cores 21-1 to 21-n are expressed as n _A1 ,
The refractive index of the lower clad on the incident side (base material 10) is n _A2 ,
The refractive index of the incident side upper cladding 31 is n _A3 ,
The refractive index of the output side core 22 is n _B1 ,
The refractive index of the output side lower cladding (base material 10) is expressed as n _B2 ,
The refractive index of the output side upper clad 32 is n _B3 ,
And when
[Example 1]
n _A2 , n _A3 ≧ n _B2 ≧ n _B3 , provided that n _A2 , n _A3 > n _B3
It is.

That is,
n _B1 = n _A1 = 1.461, n _A2 = n _A3 = n _B2 = 1.45, n _B3 = 1
Thus, the refractive index of the exit side waveguide can be set to n≈1 (air).

  As described above, the relationship between the refractive indexes of the core and the clad may be such that, for example, a part or all of the refractive index of the clad on the output side is lower than the refractive index of the clad on the incident side.

  According to this structure, since the “light confinement action” on the optical coupling side, that is, the output side waveguide is strengthened, the coupling loss is reduced without securing the width of the output side waveguide core more than necessary. . In addition, the emission-side waveguide cladding can be made of air, which is easy to manufacture.

  This can also be achieved simultaneously / or by making the refractive index of the exit-side core greater than the refractive index of the entrance-side core. That is, since the “light confinement action” at the optical coupling side, that is, the output side waveguide is strengthened, the coupling loss is reduced without securing the width of the output side waveguide core more than necessary.

For example,
[Example 2]
n _B1 > n _A1
It is.

That is,
_{n B1 = 2, n A1 =} 1.461, n A2 = n A3 = n B2 = n B3 = 1.45
Thus, the coupling loss is reduced to about ½ of [Example 1] as shown in FIG.

Also, by combining [Example 1] and [Example 2],
[Example 3]
n _A2 , n _A3 ≧ n _B2 ≧ n _B3 , provided that n _A2 , n _A3 > n _B3 , and n _B1 > n _A1
For example,
_{n B1 = 2, n A1 =} 1.461, n A2 = n A3 = n B2 = 1.45, n B3 = 1
By doing so, the coupling loss is further reduced by about 10% as compared with [Example 2] as shown in FIG.

Thus, by applying [Example 1] to [Example 3], in the optical coupler 1 shown in FIGS. 1 to 3, the respective heights of the incident-side waveguide cores 21-1 to 21-n are increased. For example, h is 6 μm, and W _{21-1 to} W _21-n are five when the width is W, each width is W _{21-1 to} W _21-n , and the width of the output-side waveguide core 22 is W _22. Even if it is 100 μm, W ₂₂ may be 100 μm.

The width _{W 22} of the outgoing side waveguide 22, when the average of the width of the incident-side waveguide core 21 - 1 to 21-n and _{W A,} Previously, it was necessary about the channel number × _{W A} In general, about W _A to (n × W _A ) / 2 is sufficient.

  Further, this configuration can be applied to all light that can be input regardless of the mode (intensity distribution) of light input to the incident waveguide and the superimposed state. The input light may be guided by an optical fiber, for example, or may be directly incident from a laser device, for example.

  FIG. 4 shows a state in which the optical coupler 1 shown in FIG. 1 is viewed from the plane direction. 5 and 6 show a state where the optical coupler 1 of FIG. 4 is cut along DD.

  As apparent from FIGS. 5 and 6, in the optical coupling portion 23 where the incident-side waveguide cores 21-1 to 21-n and the emission-side waveguide 22 in the optical waveguide structure 20 are connected, both cores are used. Are cut at a predetermined angle, for example, 8 degrees (a taper is formed) with respect to a line segment orthogonal to the direction in which the core extends (the plane direction of the base material 10). The direction in which the cut surface is inclined may be on the exit side waveguide side (FIG. 5) or on the entrance side waveguide side (FIG. 6).

  As shown in FIG. 5 and FIG. 6, in the optical coupling portion 23, a taper is formed on each cut surface of the incident-side waveguide core and the outgoing-side waveguide core, so that the return loss in the optical waveguide structure 20 is increased. Is known to be reduced. In addition, taper of each cut surface of the incident side waveguide core and the emission side waveguide core shown in FIGS. 5 and 6 is performed simultaneously with the combination of refractive indexes shown in FIGS. A further effect can be expected to reduce the coupling loss shown in the second embodiment and the third embodiment.

  Hereinafter, a method of manufacturing the optical coupler 1 shown in FIGS. 1 to 6 will be briefly described.

In FIG. 1 (or FIG. 4), a buffer layer having a predetermined thickness (not shown) is formed on a substrate 10 made of, for example, Si (silicon) or SiO ₂ (silicon oxide), and the buffer layer is formed by, for example, CVD (Chemical Vapor). By the Deposition, the members having the first refractive index used for the incident side waveguide cores 21-1 to 21-n, the emission side waveguide core 22 and the optical coupling portion 23 are deposited to a predetermined thickness ( Vapor phase growth).

  Subsequently, the first refractive material deposited in a region other than the region corresponding to the core region of each waveguide is removed by, for example, etching.

  Next, the output-side waveguide core 22 side from the boundary C (predetermined position of the optical coupling portion 23) is shielded by a mask of a predetermined shape (not shown), and the remaining core region (incident side) is formed in the remaining region. A member having a second refractive index corresponding to the first clad (incident side waveguide clad) region capable of providing a predetermined refractive index difference between the core region and the core region. For example, it is deposited to a predetermined thickness by CVD.

  In this state, the optical coupler 1 of [Example 1] is obtained.

On the other hand, from the boundary C (predetermined position of the optical coupling portion 23), either one of the portion corresponding to the incident-side waveguide cores 21-1 to 21-n or the portion corresponding to the emission-side waveguide core 22 is illustrated. However, in order to change the refractive index of the previously formed core region (compared to the remaining region) to the remaining region by shielding with a mask of a predetermined shape, for example, Ge (germanium) is adjusted to a predetermined concentration. Dope. In order to increase the refractive index, for example, P (phosphorus), Ti (titanium), or Al (aluminum) or Ti0 ₂ (titanium oxide) and the like are available.

By controlling the Ge doping amount, for example, the refractive index n ₂₁ of the incident-side waveguide core can be easily set to n ₂₁ = 1.466. The refractive index _{n 10} of the substrate 10, for example, about _n 10 = 1.450, if the outgoing side waveguide side core and n = 2.0, the incident as shown in Example 2 side waveguide core 21 - 1 to 21-n of the refractive index _{n 21} is the outgoing side waveguide smaller optical waveguide structure than the refractive index _{n 22} of the core 22 20 (optical coupler 1) is obtained.

  It goes without saying that the optical coupler 1 of [Example 3] can be obtained by combining these steps.

  Moreover, the refractive index of the output side waveguide clad 32 can also be made lower than the refractive index of the incident side waveguide clad 31 by doping B (boron) or F (fluorine), for example.

  Note that the present invention is not limited to the above-described embodiment, and various modifications or changes can be made without departing from the scope of the invention at the stage of implementation. Further, the individual embodiments may be appropriately combined as much as possible, and in that case, the effect of the combination can be obtained.

The schematic perspective view which shows an example of the optical coupler with which this invention is applied. The schematic sectional drawing which cut | disconnected the optical coupler shown in FIG. 1 by AA of FIG. The schematic sectional drawing which cut | disconnected the optical coupler shown in FIG. 1 by BB of FIG. The top view of the optical coupler shown in FIG. FIG. 5 is a schematic cross-sectional view of the optical coupler shown in FIG. 1 cut along CC in FIGS. 1 and 4. FIG. 5 is a schematic cross-sectional view of the optical coupler shown in FIG. 1 cut along CC in FIGS. 1 and 4. The graph which shows the grade of the loss of the optical coupler shown in FIG. 1 thru | or FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical coupler, 10 ... Board | substrate, 20 ... Optical waveguide structure, 21-1 to 21-n ... Incident side waveguide core, 21a ... Taper, 22 ... Outgoing side waveguide core, 22a ... Taper, 23 ... Optical coupling , 30... Cladding layer, 31... Incident side waveguide cladding, 32... Exit side waveguide cladding, C... (Of the refractive index of the optical coupling portion).

Claims (10)

A substrate;
A core region formed on the substrate;
A cladding region that gives a predetermined refractive index difference to the core region;
The core region includes a plurality of incident waveguides, a coupling portion that couples the plurality of incident waveguides, and a smaller number of outgoing waveguides than the incident waveguides connected to the coupling portion. In the optical coupler, the sum of the widths of the incident waveguides is larger than the sum of the widths of the output waveguides.
The optical coupler according to claim 1, wherein a refractive index of a part or all of the clad on the output waveguide side is smaller than a refractive index of the clad on the incident side waveguide.   The optical coupler according to claim 1, wherein the cladding region on the output waveguide side is air.   The position where the refractive index of the clad of the output side waveguide is lower than the refractive index of the clad of the input side waveguide is from the junction between the output waveguide and the coupling part to the incident side waveguide side. 3. The optical coupler according to claim 1, wherein the optical coupler is movable within a range of not more than twice the length of the portion. A substrate;
A core region formed on the substrate;
A cladding region that gives a predetermined refractive index difference to the core region;
The core region includes a plurality of incident waveguides, a coupling portion that couples the plurality of incident waveguides, and a smaller number of outgoing waveguides than the incident waveguides connected to the coupling portion. In the optical coupler, the sum of the widths of the incident waveguides is larger than the sum of the widths of the output waveguides.
The optical coupler according to claim 1, wherein a refractive index of a part or all of the core on the output waveguide side is larger than a refractive index of the core of the incident side waveguide.   The position where the refractive index of a part or all of the core on the incident waveguide side is larger than the refractive index of the core of the output waveguide is from the junction between the output waveguide and the coupling portion. 5. The optical coupler according to claim 4, wherein the optical coupler is movable to a side within a range within twice the length of the coupling portion.   The boundary part between the core on the incident waveguide side and the core on the output waveguide side has a shape (taper) that can reduce the incidence of the reflection component at the boundary part into any of the cores, The optical coupler according to claim 4 or 5. A substrate;
A core region formed on the substrate;
A cladding region that gives a predetermined refractive index difference to the core region;
The core region includes a plurality of incident waveguides, a coupling portion that couples the plurality of incident waveguides, and a smaller number of outgoing waveguides than the incident waveguides connected to the coupling portion. In the optical coupler, the sum of the widths of the incident waveguides is larger than the sum of the widths of the output waveguides.
The refractive index of a part or all of the cladding on the output waveguide side is smaller than the refractive index of the cladding of the incident side waveguide, and the refractive index of a part or all of the core on the output waveguide side is the incident side waveguide. An optical coupler having a refractive index greater than that of the core.   8. The optical coupler according to claim 7, wherein the cladding region on the output waveguide side is air.   The refractive index of a part or all of the cladding on the output waveguide side is smaller than the refractive index of the cladding of the incident side waveguide, and the refractive index of a part or all of the core on the output waveguide side is the incident side waveguide. The position larger than the refractive index of the core is movable from the junction between the output waveguide and the coupling portion to the incident-side waveguide side within a range within twice the length of the coupling portion. The optical coupler according to claim 7 or 8, characterized in that   The boundary part between the core on the incident waveguide side and the core on the output waveguide side has a shape (taper) that can reduce the incidence of the reflection component at the boundary part into any of the cores, The optical coupler according to claim 7.

Images